Mechanism of sulfur emission quenching in flame photometric detectors

Abstract

The effect of sulfur emission quenching by CH 4, CO, CO 2 and octane was studied using pulsed flame photometric detection (PFPD). It was established that quenching is more efficient at the long time delayed emission. The dependence of quenching efficiency on quencher concentration was found to be similar for all of the above compounds when it was normalized to the concentration of carbon atoms. It is proposed that the dominant reaction leading to sulfur emission quenching is CO + S = COS whereas CO is probably the main product of hydrocarbon combustion in a hydrogen-rich hydrogen-air flame. The experiments and model calculation indicate that CO-induced catalytic hydrogen recombination also promotes quenching and thus quenching is a universal phenomenon in FPD. A quenching-free dynamic range is defined; it is 10 5 for pulsed FPD. It is shown how quenching is identified and largely reduced with pulsed FPD.